Focal-plane shutter

ABSTRACT

A focal-plane shutter for a camera includes two shutter blades each of which comprises two opaque plates. At least one of the two plates has a slit and is held at two points by two arms such that the plates move like a pantograph. The arms are pivotally mounted by eccentric pins to provide for adjusting the parallelism of the blades.

This is a division of application Ser. No. 346,100, filed May 2, 1989, now U.S. Pat. No. 4,954,860.

FIELD OF THE INVENTION

The present invention relates to a focal-plane shutter for use in a camera and, more particularly, to a focal-plane shutter having two shutter blades one of which is used to open the aperture in the shutter, the other being used to close the aperture. In each shutter blade, either plural opaque plates or a least one plate forming a slit is held at two points by two arms to permit the plate or plates to move like a pantograh.

BACKGROUND OF THE INVENTION

A conventional shutter blade of the above-described structure will now be described by referring to FIGS. 3 and 4, where a shutter has a base plate 1 provided with an aperture 1a. Arms 2 and 3 are pivotally mounted to the plate 1 by shafts 4 and 5, respectively. A slit plate 6 having a slit for exposure is pivoted to the arms 2 and 3 by shafts 7 and 8, respectively. Similarly, a cover plate 9 is pivotally mounted to the arms 2 and 3 by shafts 10 and 11, respectively. The aperture 1a is covered by the slit plate 6 and the cover plate 9.

Only one of two similar shutter blades which are symmetrical with respect to a horizontal line is shown in FIGS. 3 and 4; for clarity, the other is not shown. In the condition shown in FIG. 3, the shutter blade is folded up and has moved away from the aperture 1a. In the condition shown in FIG. 4, the shutter blade is in a position to cover the aperture 1a.

When the shutter is tripped for exposure, the shutter blade is very quickly switched from the condition shown in FIG. 3 to the condition shown in FIG. 4 or vice versa. During this process, the arms 2 and 3 rotate to move the slit plate 6 and the cover plate 9 upwardly or downwardly while they are maintained in a horizontal posture.

Because of the inertia of various components and errors arising during the manufacturing process, the slit plate 6 may be inclined relative to the aperture 1a. Therefore, the plate 6 is not retained in the horizontal posture while moving. As a result, the exposure becomes non-uniform, i.e., the exposure time differs between the right portion and the left portion of the aperture. In recent years, it has been required to shorten the exposure time. With this trend, the width of the slit is reduced. Consequently, the effects of the inclination of the slit plate become more conspicuous.

SUMMARY OF THE INVENTION

In view of the foregoing drawback with the prior art device, it is an object of the invention to provide a focal-plane shutter for use in a camera and in which plate-forming slits are driven in a parallel relation to each other, whereby the exposure time is prevented from differing between the left portion and the right portion of the aperture.

The above object is achieved by a focal-plane shutter comprising two sets of shutter blades each of which consists of a plurality of opaque plates, at least one of the plates having a slit and held at two points by two arms so that the plates may move like a pantograph. The shutter is characterized in that it includes adjusting portions which adjust the inclination of the plates forming the slits.

Other objects and features of the invention will appear in the course of the description thereof which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front elevational view of the main portions of one set of blades of a focal-plane shutter according to the invention in which the blades are withdrawn;

FIG. 2 is a view similar to FIG. 1 but in which the blades are in a closed position;

FIG. 3 is a front elevational view of the main portions of one set of blades of a conventional shutter in which the blades are withdrawn;

FIG. 4 is a view similar to FIG. 3 but in which the blades are in a closed position;

FIG. 5 is a cross-sectional view, on a larger scale, of one of the pivotal supports; and

FIG. 6 is a cross-sectional view, similar to FIG. 5, but showing another position of the pivotal supports.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1 and 2, there is shown a focal-plane shutter embodying the concept of the invention. It is to be noted that like components are indicated by like reference numerals in all the figures, and that those components which have already been described in conjunction with FIGS. 3 and 4 will not be described in detail below. FIGS. 1 and 2 correspond to FIGS. 3 and 4, respectively.

In FIGS. 1, 2, 5 and 6 arm 2 has a shaft 12 consisting of an eccentric pin 12a. Plate 6 is provided with a slit. If the plate is inclined relative to apertures 1a (for example, as shown in FIG. 3); the plate 6 can be aligned with the aperture 1a by rotating the shaft 12, for example, with a turning tool (e.g., a screwdriver) inserted in the slot 12b.

In the present example, only the shaft 12 of the arm 2 comprises an eccenctric pin. However, the pivot points 7 and 8 at which the plate 6 is held by arms 2 and 3 can also be fabricated in the same manner as the shaft 12.

In the above example, an adjustment is made to prevent the plate 6 having the slit from tilting relative to the aperture 1a. It is also possible to make an adjustment so as to prevent the other plate (not shown) having a slit from tilting.

As described thus far, in accordance with the present invention, the points at which the plate are held by the arms or the pivots of the arms are each comprised of an adjustable eccentric pin. Therefore, the two slit plates are so adjusted as to move parallel to each other. Consequently, non-uniformity of exposure is decreased in that the time during which the left portion of the aperture is exposed and the time during which the right portion is exposed is more uniform. The invention is especially useful for high-speed shutters having narrow slits. 

What we claim is:
 1. A focal-plane shutter comprising a base member having an aperture, shutter blades for opening and closing said aperture, and pivotal support means on said base member operable in a parallelogrammatic configuration to move said blades between open and closed positions to thereby open and close said aperture, said pivotal support means having adjusting means for adjusting the tilt of one blade relative to another blade to provide for parallel movement of said blades and uniformity of exposure of said aperture during opening and closing of said aperture by said blades.
 2. A focal-plane shutter comprising a base plate having an aperture, two sets of shutter blades for opening and closing said aperture, said two sets of shutter blades each being provided with a plurality of opaque plates, and pivotal arm means pivotably connected to said base plate at two spaced pivot connections and pivotably connected to at least one plate of one set of shutter blades at two spaced pivot connections in a substantially parallelogrammatic configuration such that the plates are moveable between open and closed positions to thereby open and close said aperture, and adjusting means on said pivotal arm means for adjusting the orientation of one plate of one set of shutter blades relative to one plate of another set of shutter blades to provide for parallelism of said plates of said two sets of shutter blades and uniformity of exposure of said aperture as said blades open and close said aperture.
 3. A focal-plane shutter comprising a base plate having an aperture, two sets of shutter blades for opening and closing said aperture, said two sets of shutter blades each being provided with a plurality of opaque plates, a pair of arm means for pivotably supporting said plates on said base plate in a substantially parallelogrammatic configuration for movement between open and closed positions to thereby open and close said aperture, and adjusting means on said arm means and on said base plate for adjusting inclination of one plate relative to another plate to thereby provide for parallel movement of said blades as said blades open and close said aperture. 